1. Field of the Invention
This invention relates to an improved system for storing and retrieving information in flash memories, and more particularly to a system that organizes and manages data written to a flash memory.
2. Description of the Prior Art
As will be appreciated by those skilled in the art, electrically erasable and programmable read-only memories (EEPROMs) comprised of flash-type, floating-gate transistors have been described in the art and are presently commercially available. These so-called flash memories are non-volatile memories similar in functionality and performance to EPROM memories, with an additional functionality that allows an in-circuit, programmable, operation to erase blocks of the memory. In a flash memory, it is not practical to rewrite a previously written area of the memory without a preceding block erase of the area. While this invention will be described in the context of a flash memory, those skilled in the art will understand that its teachings are also applicable to data storage devices with the same write, read, and block erase before write characteristics as flash memories.
In a typical computer system, the operating system program is responsible for data management of the data storage devices that are a part of the system. A necessary, and usually sufficient, attribute of a data storage device to achieve compatibility with the operating system program is that it can read data from, and write data to, any location in the data storage medium. Thus, flash memories are not compatible with typical existing operating system programs, since data cannot be written to an area of flash memory in which data has previously been written, unless the area is first erased.
Software products have been proposed in the prior art to allow a flash memory to be managed by existing computer operating programs without modification of the operating system program. However, these prior art programs operate the flash memory as a "write once read many" device. This prior art software product cannot recycle previously written memory locations. When all locations are eventually written the memory cannot be further used without specific user intervention.